Powder spraying apparatus

ABSTRACT

In a powder spraying apparatus the powder is brought into fluidized state within a pressure vessel and in a conveying main conduit. Fluidizing is accomplished by pressure fluid acting through a sinter metal bed in the vessel and through a perforated supplementary conduit in the main conduit. When a control valve is opened, powder will flow for atomizing and coating purposes in the manner of a liquid from the pressure vessel to spray guns.

United States Patent [191 Liedberg ar. 19, R974 POWDER SPRAYING APPARATUS [75] Inventor: Kurt Herman Liedberg, Skara,

Sweden [73] Assignee: Atlas Copco Aktiebolag, Nacka,

Sweden [22] Filed: Nov. 9, 1972 [21] Appl. No.2 305,140

[30] Foreign Application Priority Data Nov. 12, 1971 Sweden 14498/71 [52] US. Cl 239/336, 239/15 [51] Int. Cl B05b 7/14 [58] Field of Search 239/15, 336

{56] References Cited UNITED STATES PATENTS 1167.541 2/1968 Cook et a1. 239/336 4/1960 Akesson 239/336 10/1967 Ross et al. 239/336 Primary Examiner-Lloyd L. King Attorney, Agent, or FirmFlynn & Frishauf [5 7] ABSTRACT In a powder spraying apparatus the powder is brought into fluidized state within a pressure vessel and in a conveying main conduit. Fluidizing is accomplished by pressure fluid acting through a sinter metal bed in the vessel and through a perforated supplementary conduit in the main conduit. When a control valve is opened, powder will flow for atomizing and coating purposes in the manner of a liquid from the pressure vessel to spray guns.

16 Claims, 2 Drawing Figures powuua sPnAwNc. APPARATUS The present invention relates to a powder spraying apparatus, and more particularly, to a powder spraying apparatus providing improved conveyance of the powder material to the spray gun.

In general, a powder spraying apparatus comprises a spray gun, a powder container and a conduit extending from the powder container to the spray gun, which conduit is connected to the spray gun for supplying powder to a spraying material passage therein. For making conveying of powder possible, the powder container as well as the conduit hitherto normally have been associated with auxiliary means for the transportation of the powder, for example comprising a dispensing gate, a vibratory conveyor and/or an ejector of which at least the ejector has been driven by means ofa gaseous pressure fluid such as compressed air. However, the prior art auxiliary means demand attendance and supervision in order to be operable and often cause operating disturbances because of the tendency of the powder to cake.

It is therefore an object of the present invention to provide a powder spraying apparatus of substantially simplified construction with respect to the auxiliary conveying means so that the apparatus will gain in dependability of operation and may be operated with a minimum of care and maintenance.

SUMMARY OF THE INVENTION In accordance with the present invention, a powder spraying apparatus includes a spray gun having a spraying material passage therein, a powder supply means and a conduit extending from the powder supply means to the spray gun, the conduit being connected to the spray gun for supplying powder to the spraying material passage therein. The improvement of the present invention resides in that the powder supply means in cludes a pressure vessel provided with a powder chamber and a pressure chamber which receives a gaseous pressure fluid. and a wall portion in the pressure vessel between the chambers. The wall portion is permeable to pressure fluid for fluidizing powder in the powder chamber by means of the pressure fluid penetrating through the permeable wall portion. The conduit has a valve associated therewith, and the inlet of the conduit is disposed in the powder chamber for conveying powder fluidized in pressure fluid to the spraying material passage in the spray gun upon actuation of the valve.

Preferably, the conduit includes a main conduit containing a perforated supplementary conduit, the perforated supplementary conduit receiving a gaseous pressure fluid. The pressure fluid penetrates into the main conduit through the perforations in the supplementary conduit to amplify the flowability of the powder when being conveyed in the conduit. The supplementary conduit is preferably a perforated tube or hose loosely inserted into the main conduit which extends over at least a substantial portion of the length of the main conduit. The supplementary conduit may extend over the whole length of the main conduit, and in practice it has been found that'satisfactory results can be achieved even if the supplementary conduit extends only over about 80 per cent of the length of the main conduit.

BRIEF DESCRIPTION OF THE DRAWING FIG. I shows a powder spraying apparatus according to the invention; and

FIG. 2 shows partly in section a part of the powder conveying conduit in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention has general application in connection with powder spraying for spreading a spray of powder particles into the surrounding atmosphere through the medium of a spraying device, such as a hand held, fixedly mounted or movably mounted spraying device. As an exemplary embodiment, there is described below a powder spraying apparatus for surface coating purposes in the form of an electrostatic paint spraying plant.

The spraying apparatus comprises a spray gun I operating on compressed air and provided with a handle 2 and a gun body 3. A trigger 4 is pivotally journalled on the gun body 3 about an axle 5 and carries an angle member 6. When the trigger 4 is pivoted about axle 5, the angle member 6 depresses the spindle of a spring load air valve 7 so that the latter opens. Simultaneously, the angle member 6 engages at the other side thereof, via a spring loaded nut sleeve 8, the spindle 9 of a needle valve 10 so as to open the latter. The air valve 7 is supplied with compressed air from a compressed air network 11 via a hose 12 and an adjustable pressure reduction valve 13. Via the air valve 7, compressed air is fed into a distributing chamber 15 and then into the passage 16 which leads to an annular slot 17 in the nozzle 18 of the spray gun 1. From the distributing chamber 15 furthermore runs a passage 20 which leads to side openings 21 in the nozzle 18 for affecting via the side openings 21 the powder spray pattern generated by the spray gun 1.

Within the nozzle 18 the needle valve 10 closes or opens the outlet of a spraying material passage 22. The needle valve 110 is terminated forwardly by a point 24 and the forward end 23 thereof is metallic or metallized by way of a coating and can be given a high electrostatic tension by an insulated high tension cable 25 which by a pin 26 is in contact with the forward end 23 of needle valve 110.

Further, the powder spraying apparatus includes a powder container 29 made as a pressure vessel and provided with a cover 30 which by means of clamps 31 is kept tightly fixed to the powder container 29. A wall 32 traverses the powder container 29 and comprises a wall portion 28 of porous air permeable material, for example a disk of sintered metal. The wall 32 divides the powder spraying container 29 into a powder chamber 33 and a pressure chamber 34. The pressure chamber 34 is supplied with compressed air from the network 11 via an adjustable pressure reduction valve 35 and a conduit 36 which connects to a bottom nipple 37 at the bottom of the powder container 29. To the cover 30 is affixed by the aid of a lead-in sleeve 38, a packing nut 40, and a packing 41, a conveying conduit 42 preferably in the shape of a flexible hose which by an open end thereof projects into the powder chamber 33 and at the other end thereof is connected to a nipple 43 which communicates with the spraying material passage 22 in the spray gun I.

A supplementary conduit 44, preferably in the shape of a flexible hose of smaller diameter than the conveying conduit 42, passes at one open end 48 thereof through a lead-in sleeve 45, a packing nut 46 and a packing 47 which are affixed to the wall portion 28. The supplementary conduit 44 is slipped and loosely placed into the conveying conduit 42 along substantially the whole or at least the greater part of the length thereof. The end of the supplementary conduit 44 within the conveying conduit 42 is closed by a plug 53 as shown in FIG. 1 near the nipple 43. Along the whole length thereof the supplementary conduit 44 is provided with perforations in the shape of fine bore holes 50, preferably in the order of 1 mm in diameter or smaller. The holes 50 are preferably evenly spaced along the length of the additional conduit 44, for example with a spacing of 30-50 mm.

Before spraying, the pressure reduction valves 13 and 35 are adjusted so that a suitable conveying and spray forming pressure isreceived at the air valve 7 in the spray gun 1, and a suitable conveying and fluidizing pressure is created in the chambers 33, 34 of the powder container 29. The high voltage cable 25 of the spray gun I is connected to a conventional electrostatic high voltage generator, not shown. For purposes of being coated by powder, diagrammatically illustrated workpieces 51 are supplied by means of a conveyor 52 to a suitably arranged working place for the gun I.

When the trigger of the spray gun I is depressed, the angle member 6 opens the needle valve 10 and the air valve 7. Because of the resultant pressure drop in the spraying material passage 22, there is pressed, by means of air pressure prevailing in the pressure chamber 34 and the powder chamber 33, powder from the powder chamber 33 into the conveying conduit 42 via the open end of conduit 42 above the wall portion 28. Also, due to the pressure drop. fluidizing air finely distributed by the micropores of the sintered material from the pressure chamber 34 is pressed through the wall portion 28 into the powder mass thereabove so that the powder receives an easily flowable substantially airborne or hovering consistency when it enters into the conduit 42. Simultaneously compressed air penetrates as flne sprays out through the holes or bores 50 along the length of the supplementary conduit 44. Unless the conduit 42 through previous operation already is filled by powder, it will at the starting period be filled by fluidized powder. The powder, which is present in the conduit 42 of which enters thereinto, respectively is fluidized or stays fluidized by the air sprays from the bores 50 of the supplementary conduit 44. Consequently, powder is conveyed in a freely floating fluidized condition over the entire transportation distance up to the spraying material passage in the spray gun 1. Practice has shown that if the supplementary conduit 44 extends forward or upstream to the vicinity of the spray gun I over the greater part of the length of the conduit 42, at least over 80 per cent of the length thereof, then the powder will maintain its good flowability the remaining distance through the spraying material passage 22 on to the needle valve 10.

During the passage of the material through needle valve 10 there if performed in a conventional way at the tip 24 an electrostatic loading of the outwardly flowing fluidized powder simultaneously with compressed air flowing out from the annular slot 17, giving the powder particles the desired velocity in the direction of the workpiece 51. Simultaneously, compressed air is flowing out via the side openings 21 and is regulated by means of the valve 19 to the desired degree so that the spray of powder particles leaving the spray gun I has a suitable spraying pattern.

The powder spraying apparatus according to the present invention is not restricted to the embodiment shown, but has general applicability. The invention is useful for example, for surface coating with or without use of control air out of the openings 17, 21 and with or without electrostatic charging of the powder particles for purposes of decoration or insulation, coating with abrading granules or stone grit, or powdering of diverse objects for medical, zoological or botanical use.

I claim:

1. A powder spraying apparatus comprising a spray gun having a spraying material passage therein, a powder supply means and a conduit extending from the powder supply means to the spray gun, said conduit being connected to the spray gun for supplying powder to said spraying material passage therein, the improvement wherein:

said powder supply means includes: a pressure vessel provided with a powder chamber and a pressure chamber receiving a gaseous pressure fluid; and a wall portion in said pressure vessel between said chambers, said wall portion being permeable to pressure fluid for fluidizing powder in the powder chamber by means of pressure fluid penetrating through said wall portion;

a valve is associated with said conduit, and the inlet of said conduit is disposed in the powder chamber for conveying powder fluidized in pressure fluid to said spraying material passage upon actuation of said valve; and

said conduit includes a main conduit containing a perforated supplementary conduit for a'gaseous pressure fluid, the pressure fluid penetrating into said main conduit from said supplementary conduit through the perforations thereof to thereby amplify the flowability of the powder when being conveyed in the conduit.

2. Apparatus according to claim 1 wherein one end of said supplementary conduit is connected to said pressure chamber in said pressure vessel.

3. Apparatus according to claim 1 wherein said supplementary conduit is a perforated hose loosely inserted into said main conduit.

4. Apparatus according to claim 2 wherein said supplementary conduit is a perforated hose loosely inserted into said main conduit.

5. Apparatus according to claim 1 wherein said supplementary conduit extends over at least a substantial portion of the length of said main conduit, said main conduit extending between said pressure vessel and said spray gun.

6. Apparatus according to claim 2 wherein said supplementary conduit extends over at least a substantial portion of the length of said main conduit, said main conduit extending between said pressure vessel and said spray gun.

7. Apparatus according to claim 6 wherein the end of said supplementary conduit remote from said pressure vessel is plugged.

8. A powder spraying apparatus comprising a spray gun having a spraying material passage therein, a powder supply means and a conduit extending from the powder supply means to the spray gun, said conduit being connected to the spray gun for supplying powder to said spraying material passage therein, the improvement wherein:

a valve is associated with said conduit; and said powder supply means includes: a pressure vessel provided with a pressure chamber receiving a pressurized gaseous pressure fluid and a powder chamber for maintaining the powder therein under pressure, the inlet of said conduit being disposed in said pressurized powder chamber; and a wall portion in said pressure vessel between said chambers, said wall portion being permeable to pressure fluid for enabling said chambers to be at substantially the same pressure and for fluidizing powder in the powder chamber by means of pressure fluid penetrating through said wall portion upon actuation of said valve, thereby conveying powder fluidized in pressure fluid through said conduit to said spraying material passage upon actuation of said valve.

9. Apparatus according to claim 1 wherein said conduit includes a main conduit containing a perforated supplementary conduit for a gaseous pressure fluid, the pressure fluid penetrating into said main conduit from said supplementary conduit through the perforations thereof to thereby amplify the flowability of the powder when being conveyed in the conduit.

10. Apparatus according to claim 9 wherein one end of said supplementary conduit is connected to said pressure chamber in said pressure vessel.

1 1. Apparatus according to claim 9 wherein said supplementary conduit is a perforated hose loosely inserted into said main conduit.

12. Apparatus according to claim 10 wherein said supplementary conduit is a perforated hose loosely inserted into said main conduit.

13. Apparatus according to claim 9 wherein said supplementary conduit extends over at least a substantial portion of the length of said main conduit, said main conduit extending between said pressure vessel and said spray gun.

14. Apparatus according to claim 10 wherein said supplementary conduit extends over at least a substantial portion of the length of said main conduit, said main conduit extending between said pressure vessel and said spray gun.

15. Apparatus according to claim 14 wherein the end of said supplementary conduit remote from said pressure vessel is plugged.

16. Apparatus according to claim 8 wherein said pressure chamber is located below said powder cham- 

1. A powder spraying apparatus comprising a spray gun having a spraying material passage therein, a powder supply means and a conduit extending from the powder supply means to the spray gun, said conduit being connected to the spray gun for supplying powder to said spraying material passage therein, the improvement wherein: said powder supply means includes: a pressure vessel provided with a powder chamber and a pressure chamber reCeiving a gaseous pressure fluid; and a wall portion in said pressure vessel between said chambers, said wall portion being permeable to pressure fluid for fluidizing powder in the powder chamber by means of pressure fluid penetrating through said wall portion; a valve is associated with said conduit, and the inlet of said conduit is disposed in the powder chamber for conveying powder fluidized in pressure fluid to said spraying material passage upon actuation of said valve; and said conduit includes a main conduit containing a perforated supplementary conduit for a gaseous pressure fluid, the pressure fluid penetrating into said main conduit from said supplementary conduit through the perforations thereof to thereby amplify the flowability of the powder when being conveyed in the conduit.
 2. Apparatus according to claim 1 wherein one end of said supplementary conduit is connected to said pressure chamber in said pressure vessel.
 3. Apparatus according to claim 1 wherein said supplementary conduit is a perforated hose loosely inserted into said main conduit.
 4. Apparatus according to claim 2 wherein said supplementary conduit is a perforated hose loosely inserted into said main conduit.
 5. Apparatus according to claim 1 wherein said supplementary conduit extends over at least a substantial portion of the length of said main conduit, said main conduit extending between said pressure vessel and said spray gun.
 6. Apparatus according to claim 2 wherein said supplementary conduit extends over at least a substantial portion of the length of said main conduit, said main conduit extending between said pressure vessel and said spray gun.
 7. Apparatus according to claim 6 wherein the end of said supplementary conduit remote from said pressure vessel is plugged.
 8. A powder spraying apparatus comprising a spray gun having a spraying material passage therein, a powder supply means and a conduit extending from the powder supply means to the spray gun, said conduit being connected to the spray gun for supplying powder to said spraying material passage therein, the improvement wherein: a valve is associated with said conduit; and said powder supply means includes: a pressure vessel provided with a pressure chamber receiving a pressurized gaseous pressure fluid and a powder chamber for maintaining the powder therein under pressure, the inlet of said conduit being disposed in said pressurized powder chamber; and a wall portion in said pressure vessel between said chambers, said wall portion being permeable to pressure fluid for enabling said chambers to be at substantially the same pressure and for fluidizing powder in the powder chamber by means of pressure fluid penetrating through said wall portion upon actuation of said valve, thereby conveying powder fluidized in pressure fluid through said conduit to said spraying material passage upon actuation of said valve.
 9. Apparatus according to claim 1 wherein said conduit includes a main conduit containing a perforated supplementary conduit for a gaseous pressure fluid, the pressure fluid penetrating into said main conduit from said supplementary conduit through the perforations thereof to thereby amplify the flowability of the powder when being conveyed in the conduit.
 10. Apparatus according to claim 9 wherein one end of said supplementary conduit is connected to said pressure chamber in said pressure vessel.
 11. Apparatus according to claim 9 wherein said supplementary conduit is a perforated hose loosely inserted into said main conduit.
 12. Apparatus according to claim 10 wherein said supplementary conduit is a perforated hose loosely inserted into said main conduit.
 13. Apparatus according to claim 9 wherein said supplementary conduit extends over at least a substantial portion of the length of said main conduit, said main conduit extending between said pressure vessel and said spray gun.
 14. Apparatus according to claim 10 wherein said supplementary conduit extends over at least a substantial portion of the length of said main conduit, said main conduit extending between said pressure vessel and said spray gun.
 15. Apparatus according to claim 14 wherein the end of said supplementary conduit remote from said pressure vessel is plugged.
 16. Apparatus according to claim 8 wherein said pressure chamber is located below said powder chamber. 